Other than your own car, RobertQ is the best way to get to DTW from SW-Ontario.

You can catch RobertQ from a couple of places in London, and you can also catch them from YYZ. If you are in Toronto and can have someone take you to Pierson, I highly recommend that. I'm not sure where RobertQ picks up people in Windsor to take them to DTW (maybe it is near the tunnel entrance?). They used to cross over at the tunnel and come back over the bridge.